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Journal ArticleDOI

Pentaquark and Tetraquark states

TL;DR: Recently, the LHCb collaboration not only confirmed the existence of the hidden-charm pentaquarks, but also provided strong evidence of the molecular picture as discussed by the authors, where the authors reviewed the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years.
About: This article is published in Progress in Particle and Nuclear Physics.The article was published on 2019-03-28 and is currently open access. It has received 465 citations till now. The article focuses on the topics: Tetraquark & QCD sum rules.
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Journal ArticleDOI
TL;DR: A review of the progress in the field of exotic $XYZ$ hadrons can be found in this article, with a summary on future prospects and challenges, as well as a survey of the current state-of-the-art.
Abstract: The quark model was formulated in 1964 to classify mesons as bound states made of a quark-antiquark pair, and baryons as bound states made of three quarks. For a long time all known mesons and baryons could be classified within this scheme. Quantum Chromodynamics (QCD), however, in principle also allows the existence of more complex structures, generically called exotic hadrons or simply exotics. These include four-quark hadrons (tetraquarks and hadronic molecules), five-quark hadrons (pentaquarks) and states with active gluonic degrees of freedom (hybrids), and even states of pure glue (glueballs). Exotic hadrons have been systematically searched for in numerous experiments for many years. Remarkably, in the past fifteen years, many new hadrons that do not exhibit the expected properties of ordinary (not exotic) hadrons have been discovered in the quarkonium spectrum. These hadrons are collectively known as $XYZ$ states. Some of them, like the charged states, are undoubtedly exotic. Parallel to the experimental progress, the last decades have also witnessed an enormous theoretical effort to reach a theoretical understanding of the $XYZ$ states. Theoretical approaches include not only phenomenological extensions of the quark model to exotics, but also modern non-relativistic effective field theories and lattice QCD calculations. The present work aims at reviewing the rapid progress in the field of exotic $XYZ$ hadrons over the past few years both in experiments and theory. It concludes with a summary on future prospects and challenges.

298 citations

Journal ArticleDOI
TL;DR: In this paper, the invariant mass spectrum of the LHCb collision data at center-of-mass energies of 7, $8, $13, and $13\mathrm{\,TeV} was studied.
Abstract: Using proton-proton collision data at centre-of-mass energies of $\sqrt{s} = 7$, $8$ and $13\mathrm{\,TeV}$ recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of $9\mathrm{\,fb}^{-1}$, the invariant mass spectrum of $J/\psi$ pairs is studied. A narrow structure around $6.9\mathrm{\,GeV/}c^2$ matching the lineshape of a resonance and a broad structure just above twice the $J/\psi$ mass are observed. The deviation of the data from nonresonant $J/\psi$-pair production is above five standard deviations in the mass region between $6.2$ and $7.4\mathrm{\,GeV/}c^2$, covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow $X(6900)$ structure are measured assuming a Breit--Wigner lineshape.

204 citations

Journal ArticleDOI
Daniele Paolo Anderle1, V. Bertone2, Xu Cao3, Lei Chang4, Ningbo Chang5, Gu Chen6, Xurong Chen3, Zhuojun Chen7, Zhu-Fang Cui8, Ling-Yun Dai7, Weitian Deng9, Minghui Ding10, Xu Feng11, Chang Gong11, Long-Cheng Gui12, Feng-Kun Guo3, Chengdong Han3, J. J. He13, Tie-Jiun Hou14, Hongxia Huang13, Yin Huang15, Krešimir Kumerički16, L. P. Kaptari3, L. P. Kaptari17, Demin Li18, Hengne Li1, Minxiang Li3, Minxiang Li19, Xue-Qian Li4, Y. T. Liang3, Zuotang Liang20, Chen Liu20, Chuan Liu11, Guoming Liu1, Jie Liu3, Liuming Liu3, X. Liu19, Tiehui Liu20, Xiaofeng Luo21, Zhun Lyu22, Bo-Qiang Ma11, Fu Ma3, Jian-Ping Ma3, Yu-Gang Ma23, Yu-Gang Ma3, Lijun Mao3, C. Mezrag2, Hervé Moutarde2, Jialun Ping13, Si-Xue Qin24, Hang Ren3, Craig D. Roberts8, Juan Rojo25, Guodong Shen3, Chao Shi26, Qintao Song18, Hao Sun27, Paweł Sznajder, Enke Wang1, Fan Wang8, Qian Wang1, Rong Wang3, Ruiru Wang3, Taofeng Wang28, Wei Wang29, Xiaoyu Wang18, Xiaoyun Wang30, Jia-Jun Wu3, Xing-Gang Wu24, Lei Xia31, Bo-Wen Xiao32, Bo-Wen Xiao21, Guoqing Xiao3, Ju Jun Xie3, Ya-Ping Xie3, Hongxi Xing1, Hu-Shan Xu3, Nu Xu21, Nu Xu3, Shu-Sheng Xu33, Mengshi Yan11, Wenbiao Yan31, Wencheng Yan18, Xinhu Yan34, Jiancheng Yang3, Yi Bo Yang3, Zhi Yang35, De-Liang Yao7, Z. Ye36, Pei-Lin Yin33, C.-P. Yuan37, Wenlong Zhan3, Jianhui Zhang38, Jinlong Zhang20, Pengming Zhang39, Yifei Zhang31, Chao Hsi Chang3, Zhenyu Zhang40, Hongwei Zhao3, Kuang Ta Chao11, Qiang Zhao3, Yuxiang Zhao3, Zhengguo Zhao31, Liang Zheng41, Jian Zhou20, Xiang Zhou40, Xiaorong Zhou31, Bing-Song Zou3, Liping Zou3 
TL;DR: In this article, an Electron-ion collider in China (EicC) has been proposed, which will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy ion Accelerator Facility (HIAF), together with a new electron ring.
Abstract: Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a polarization of ∼80%) and protons (with a polarization of ∼70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2–3) × 10$^{33}$ cm$^{−2}$ · s$^{−1}$. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC.The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies.This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.[graphic not available: see fulltext]

154 citations

Journal ArticleDOI
TL;DR: In this paper, a review of threshold cusps and various triangle singularities in hadronic reactions, paying attention to their manifestations in phenomena related to exotic hadron candidates is presented.

113 citations

References
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Journal ArticleDOI
TL;DR: The complete review as discussed by the authors is published online on the website of the Particle Data Group (http://pdg.lbl.gov) and in a journal. Volume 1 is available in print as thePDG Book.
Abstract: The complete Review(both volumes) is published online on the website of the Particle Data Group(http://pdg.lbl.gov) and in a journal. Volume 1 is available in print as thePDG Book. AParticle Physics Bookletwith the Summary Tables and essential tables, figures, and equations from selected review articles is also available.

6,464 citations

Journal ArticleDOI
TL;DR: In this paper, a systematic study is made of the non-perturbative effects in quantum chromodynamics, where the basic object is the two-point functions of various currents and the terms of this series are shown to be of two distinct types.

3,874 citations

Journal ArticleDOI
TL;DR: The three quark system is studied in a relativized version of the quark potential model with chromodynamics and the spectrum of baryons is described with parameters consistent with those of an analogous study of meson spectroscopy.
Abstract: We have studied the three quark system in a relativized version of the quark potential model with chromodynamics. With parameters consistent with those of an analogous study of meson spectroscopy we obtain a successful description of the spectrum of baryons. The model naturally explains the apparent absence of spin‐orbit interactions in baryons.

2,203 citations

Journal ArticleDOI
TL;DR: In this paper, a new mathematical framework for the Wess-Zumino chiral effective action is described, and it is shown that this action obeys an a priori quantization law, analogous to Dirac's quantization of magnetic change.

2,132 citations

Journal ArticleDOI
Edward Witten1
TL;DR: In this article, the existing results concerning mesons and glue states in the large-N limit of QCD are reviewed, and it is shown how to fit baryons into this picture.

1,934 citations